1. Field of the Invention
The present invention relates to a semiconductor luminescent element capable of emitting light by virtue of an exciton and, in particular, relates to a semiconductor luminescent element which is formed by using an epitaxial ZnO film and which has wave lengths in a range from blue light to ultraviolet light, and to a method of manufacturing the same.
2. Description of the Related Art
In recent years, there have been a demand for developing a multi-color luminescent display and a demand for improving a data density with respect to data communication and data recording. Therefore, there is a strong need to produce a semiconductor luminescent element having wave lengths in a range from blue light to ultraviolet light. As a material for forming a semiconductor luminescent element capable of emitting blue light, people have been interested in a semiconductor material based on the GaN system. But, since there are many technical problems in the process for manufacture such a semiconductor material, this material has not been put into practical use. Accordingly, the inventors have suggested using ZnO which can serve as a semiconductor material having wave lengths in a range from blue light to ultraviolet light, thereby making it possible to substitute such a material for a GaN system material. More specifically, to use ZnO, a ZnO film is allowed to grow epitaxially on a substrate plate. With the use of such epitaxial film, it has been tried to obtain a luminescent element which is capable of effecting a light emission by virtue of an exciton in the vicinity of a wave length of 370 nm.
However, there have been the following problems with the above semiconductor luminescent element formed by using the above ZnO film. Namely, the ZnO film to be used as a luminescent layer (hereinafter referred to as a ZnO luminescent layer) has to have an extremely excellent crystallinity. But, the formation of such ZnO luminescent layer is extremely difficult. Conventionally, ZnO film is used in various electronic devices. If it is a polycrystal ZnO film having only a relatively low crystallinity, it can be easily manufactured in a large amount with the use of a sputtering method. Further, if a sapphire substrate is used as a substrate plate, a film formation method may be employed to form ZnO epitaxial film by virtue of the sputtering treatment. However, the epitaxial ZnO film formed with the use of the above method does not have a satisfactory orientation, hence making it impossible to provide a good crystallinity which is required in forming a luminescent element. For this reason, in order to form a ZnO luminescent layer which can be used as a luminescent element, it is necessary to use a sapphire substrate as a substrate plate, and to use an expensive and delicate film formation method such as a Laser MBE (Molecular Beam Epitaxy) method. However, such a film formation method is extremely limited in its use. Further, even using the above discussed method one is still not sure of being able to reproducibly obtain a ZnO luminescent film having a fully satisfactory film quality. In addition, with the Laser MBE method, an obtainable area of the ZnO luminescent layer is extremely small, i.e., at most several square millimeters. Moreover, a speed for the formation of the film is slow, making the method not suitable for an industrial mass production.
Therefore, it is an object of the present invention to provide a semiconductor luminescent element having a ZnO luminescent layer exhibiting a satisfactory crystallinity as a luminescent element.
Another object is to provide a method capable of reproducibly manufacturing such element on a mass production scale.
The foregoing and other objects are achieved in accordance with certain aspects of the invention by a semiconductor luminescent element which comprises: a base substrate; a ZnO luminescent layer formed on the base substrate; and a ZnO buffer layer doped with an impurity and formed between the base substrate and the ZnO luminescent layer.
The base substrate is preferably made of a material selected from the group consisting of sapphire, quartz, silicon, glass and fused quartz. The impurity is preferably selected from the group consisting of Li, Cu, Ni, Y, Ag, Mn, Mg, Al, V, Fe, La, Ti, Ta, Nb and Ga.
According to the present invention, it is possible to manufacture, with the use of a relatively easy method, such as a sputtering method, and with a high productivity, a ZnO luminescent layer having a good orientation/crystallinity suitable for use as a luminescent element which was difficult to manufacture in the past.
For the purpose of illustrating the invention, there is shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.